1. Field of the Invention
The present invention relates to a voltage-sourced HVDC system having a modulation function, and more particularly to a PWM-based voltage-sourced HDVC device.
2. Description of the Related Art
In a High-Voltage Direct Current (HVDC) scheme among DC power transmission schemes, AC power generated by a power plant is converted into DC power and the DC power is transmitted to a power receiving side which receives and converts the transmitted DC power back into AC power and supplies the AC power. This power transmission scheme enables economical power transmission through voltage boosting, which is an advantage of the conventional AC power transmission technology, while overcoming a number of problems of AC power transmission.
Such an HVDC scheme can be classified into a current-sourced HVDC scheme that uses a thyristor and an HVDC scheme that uses an IGBT or GTO. The current-sourced HVDC scheme is suitable for large-capacity power transmission and the voltage-sourced HVDC scheme is suitable for small-capacity power transmission or grid stabilization due to high loss. The voltage-sourced HVDC scheme can be classified into a phase control scheme and a PWM scheme according to driving method. While the phase control scheme is similar to the current-sourced scheme, the phase control scheme has a self-communicated function.
FIG. 1 is a schematic block diagram of a voltage-sourced HVDC system. In FIG. 1, reference numeral 11 denotes a rectifier that converts AC to DC, reference numeral 12 denotes an inverter that converts DC to AC. In FIG. 1, reference numerals 13 and 14 denote a general AC grid.